Nigeria's Economic and Financial Crimes, the country's leading anti-graft agency, says highly classified documents relating to what is described as "a very sensitive matter" were stolen over the weekend. 

The Economic and Financial Crimes Commission, known as the EFCC, says unknown people broke into its operational office in Abuja and stole what it referred to as vital documents relating to an ongoing investigation involving an unnamed prominent Nigerian.

EFCC spokesman Osita Nwajah, says sufficient safeguards were put in place and the incident would not affect current investigations.

"Of course we have our suspicions but we would not be able to make that public now so that we don't jeopardize our investigations. We operate in teams. For instance team A is working on a particular investigation, the central operation office would have the documents," he said. "We do not pass on the original documents to the teams. We make copies of that something to the teams. It is the copy that was made available to the team that got missing. So it is not going to affect our investigation. But we understand that there is a problem if certain people are targeting your office to steal certain documents. So that is an operational hiccup which we are dealing with."

The EFCC is waging a high -profile campaign against graft in Nigeria, which is considered the sixth-most-corrupt country by independent watchdog Transparency International.

The EFCC has secured fraud convictions against some corrupt officials and others, including those who stole $242 million from a Brazilian bank.

Critics say it has been politically manipulated as a weapon against opponents of President Olusegun Obasanjo, but the agency denies this.

Spokesman Nwajah says the EFCC will frustrate corrupt politicians from running for office during the 2007 general elections.

"Now what EFCC is going to do, is not only to tell the electorates this is what this person has done, we are going to take such an individual to court, where whatever evidence we have, will be tendered and used to prosecute the person," added Nwajah. "After we have done all of these, it is the business of the political parties, if they still want to go ahead and field that candidate, they are very free."

EFCC says about two thirds of Nigeria's 36 state governors would have been facing corruption charges, if they did not have immunity. The agency has reportedly seized about $5 billion from corrupt officials and criminal gangs in Nigeria in the past three years.